With the emergence of high-capacity services, the optical communication system has the evolution tendency from 10 Gb/s to 40 Gb/s, 100 Gb/s, or higher rates. However, as the rate increases, the pulse period is shortened and the effect of the chromatic dispersion (CD, chromatic dispersion) magnifies quadratically. To achieve a high transmission rate, coherent optical communications technologies are introduced to the high-speed optical transmission. In a coherent optical communications system, the chromatic dispersion can be compensated effectively by using the electronic chromatic dispersion compensation technology.
By combining the polarization multiplexing with the coherent reception technology, long-distance transmission of above 100 Gb/s may be achieved. FIG. 1 shows a typical polarization multiplexing coherent receiver. As shown in FIG. 1, a received optical signal is split by a polarization beam splitter 101 into an x path of a signal and a y path of a signal, the signals are fed into 90° frequency mixers 103x and 103y respectively, and then the signals pass through a photodetector 104 (indicated as PD in FIG. 1) and an analog-to-digital conversion module 105 (indicated as A/D in FIG. 1) to obtain digital signals Ix, Qx, Iy, and Qy through N times of sampling (N is 2 normally). The signals are input into a chromatic dispersion compensation module 106x at the x path and a chromatic dispersion compensation module 106y at the y path respectively, so that the chromatic dispersion compensation is completed. After the chromatic dispersion compensation, the signals are input into a polarization compensation module 107 formed by 2*2 butterfly filters to complete polarization demultiplexing and equalizing. After the equalizing, the signals are input into phase recovery modules 108x and 108y and decoding modules 109x and 109y respectively to recover the original bit stream. To track the rapid change of a channel, an adaptive filter is usually used for the polarization compensation module 107. A coefficient update module 110 is configured to update a coefficient of the filter of the polarization compensation module 107 in real time. However, when the chromatic dispersion compensation module performs the chromatic dispersion compensation, it needs to foresee a chromatic dispersion value to determine a compensation transfer function. When the chromatic dispersion value is unknown, an existing architecture needs to scan all kinds of possible chromatic dispersion values in an electric layer to find a chromatic dispersion value that makes a certain pointer (such as BER/Q) optimal so as to compensate the chromatic dispersion value.
It can be seen from the above description that, all kinds of possible chromatic dispersion values in the electric layer need to be scanned when the chromatic dispersion compensation is performed in the prior art. The operation flow is complicated, thereby reducing the speed of the compensation algorithm.